The Kármán line is the international boundary of space, located 100km above the Earth’s surface. The US defines it as 50 miles above the surface. It was named after Theodore von Kármán, who calculated that above 100km, an aircraft must travel faster than orbital speed to stay high. Beyond 100km, it becomes possible to orbit the Earth.
The Kármán line is the international definition for the boundary of space. It is located 100km (62 miles) above the earth’s surface, around where the northern lights form. The only country that adopts its own alternative definition is the United States, which defines the boundary of space as 50 miles (80 km) above the earth’s surface. The international aeronautical and astronautics body that supports the Kármán line is the Fédération Aéronautique Internationale (FAI).
The idea of the Kármán line originates from Theodore von Kármán, a Hungarian-American physicist who calculated that above about 100 km in the atmosphere, the air becomes so thin that an aircraft must travel faster than that orbital to stay high. This is too subtle for aeronautical purposes and, as such, activity above 100km is demarcated as astronautics rather than aeronautics.
Another factor in placing the Kármán line where it is is its proximity to the mesosphere-thermosphere boundary, which is approximately 85 km 53 miles). The thermosphere is so named because it is hotter than the layers below it, due to ionizing ultraviolet radiation from the Sun. Although local temperatures in some parts of the thermosphere can exceed the temperature of the fire, you could be outdoors in the region in a suit spatial, because the atoms are so far apart that their energy is not a real issue. Above, the thermosphere, in the ionosphere, ionizing radiation is so prevalent that the entire layer is charged, which allows radio waves to bounce off it.
Beyond 100 km is when it becomes possible to orbit the Earth, although it is easier and safer around 220 km (137 miles), where we can find the International Space Station. Orbits below the Kármán line degrade rapidly, approaching or slamming into the surface of the Earth. Beyond 100 km, a sustained orbit is possible, although orbital speed must be maintained to avoid degradation. When the Kármán line was established, a number of scientists made the relevant calculations to determine where the line lay, and when the results agreed on 100 km, they eagerly accepted it as the official demarcation. The fact that 100 km is an easy-to-remember number helped it for its future designation as the Kármán Line.
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